Phosphors function as a vehicle converting energy of an excitation source into energy of visible light and are essential elements to realize a variety of display device images. At the same time, efficiency and color reproduction range of phosphors are important elements directly related to efficiencies and color reproduction ranges of display products and lighting products.
Blue LED devices are diode devices emitting white light. In Blue LED devices, a phosphor emitting blue light as an excitation source to yellow light is coated over a device emitting blue light, to realize white light by mixing blue light emitted from the device and yellow light emitted from the phosphor. That is, LED devices emitting white light use blue light emitted from a device and a second light source, by coating a phosphor over an LED, and, in general, a YAG:Ce phosphor emitting yellow light is coated over a blue LED to generate white light [U.S. Pat. No. 6,069,440].
However, the method has drawbacks such as quantum deficits occurred by using second light, efficiency reduction due to reradiation efficiency, and uneasy color rendering. Therefore, conventional white LED backlights manufactured by combining a blue LED chip and a yellow phosphor express unnatural color due to deficiency of green and red color ingredients and, as such, applications thereof are limited to screens of mobile phones and laptop PCs. Despite such advantages, the method is broadly used due to advantages such as easy driving and dramatically low price.
Meanwhile, regarding white LED, phosphors emitting visible light by being excited by excitation sources having high energy such as ultraviolet light, blue light or the like have been mainly developed. However, conventional phosphors have deteriorated luminance when exposed to an excitation source. Accordingly, recently, as phosphors having reduced luminance deterioration and using silicon nitride-related ceramics as a host crystal, nitrides or phosphors which have a stable crystal structure and may shift excitation light or luminescence to a longer wavelength have attracted attention.
In particular, a CaAlSiN3:Eu red phosphor was developed in 2004 and a β-SiAlON:Eu green phosphor was developed in 2005, as pure nitrides. When such phosphors are combined with a blue LED chip, light having superior color purity is emitted, in particular, small temperature change due to excellent durability is exhibited and, as such, lifespan and reliability of an LED light source may be improved.
A recently developed lighting LED combined after improving a blue LED chip, a Lu3Al5O12:Ce green phosphor, and a CaAlSiN3:Eu red phosphor such that three primary color ingredients may be generated by converting light having a wavelength of 450 nm into a green or yellow phosphor having a wavelength of 520 to 570 nm, or a red phosphor having a wavelength of 650 nm. However, by such combination, it is not easy to maintain color rendering of 90 or more, and a relatively large amount of a red phosphor is required to select a proper white coordinate and, as such, luminous intensity may be lowered.
Meanwhile, research into acid nitride phosphors has been performed since 2009, but lattice defects frequently occur due to bonding of unstable oxygen ions and nitrogen ions and thereby the acid nitride phosphors are not trusted, and, accordingly, commercialization is being delayed.
Accordingly, Korean Patent Pub. Nos. 2011-0016377 and 013-00283742 disclose that a crystal field surrounding Eu ions has a large impact on a central luminescence wavelength of a SiON-based phosphor activated by Eu, and a phosphor has excellent temperature stability and temperature characteristics by optimizing ingredients of cations and anions, and a composition ratio thereof. Here, a primary luminescence wavelength of the phosphor is 540 to 570 nm.
However, until now, it has been difficult to determine how a crystal structure change of such an acid nitrides phosphor and light properties are connected [International Publication No. 2007/096333 and Chemistry of Materials, 25, pages 1852 to 1857, 2013].
Accordingly, the present inventors tried to resolve the conventional problems and, as a result, confirmed that when ingredients of cations and anions, and a composition ratio thereof are optimized, a highly efficient and stable bluish green luminescence phosphor may be provided by minimizing lattice defects in a homogeneous phase and a multi-phase crystal structure at thermodynamic synthetic temperature, and, when a white LED obtained by coating a mixed green phosphor and red phosphor over a conventional blue LED is prepared, a white LED device is manufactured by mixing a bluish green luminescence phosphor according to the present invention therewith and thereby a color rendering index and luminous intensity of a manufactured white LED device are improved, thus completing the present invention.